Non-contact temperature measurement instruments are well known for their ability to sense infrared (IR) radiation emanating from a target in order to provide an operator with useful information about the temperature of the target. Such familiar temperature measurement instruments include, for example, devices such as single-spot IR detectors and thermal imagers employing multiple arrayed detector elements.
A non-contact temperature sensing instrument cannot always see an entire target, but receives infrared radiation from a measurement area or spot on a target within the instrument's field of view. The field of view is usually defined by properties of the instrument's infrared detector, focusing optics, and distance from the target. As the instrument is moved relative to the target, different areas of the target come within the instrument's field of view. Thus, for example, an operator can pan an instrument across a large target surface to separately view different areas of the target.
Temperature measurement instruments include a variety of feedback devices for providing temperature information. For example, a single-spot IR detector often includes a simple digital display that displays a single temperature reading for the measured target. Other instruments, such as thermal imagers, provide a more complex display, such as a liquid crystal display (LCD) or plasma image display. Such displays can allow the operator to view a complete thermal image of the target on the display.
Although these and other types of displays provide a wealth of temperature information about a target, it is not always clear how the temperature information correlates to different areas of the target. For example, an instrument with only a numerical temperature readout relies on an operator to visually correlate the temperature reading with the measured area of the target. As will be appreciated, it can be difficult to determine how temperature readings correspond to different areas of a target, because it is not always clear where the instrument is pointing.
Some temperature detectors employ one or more laser beams to aid an operator in aiming the instrument. For example, some temperature measurement instruments include a laser beam sighted along the center of the instrument's field of view. Such a laser beam can illuminate the center of the instrument's measurement spot on a target, thus allowing an operator to move the instrument and easily determine where the instrument is pointed. Other temperature detectors include a variety of laser sighting devices that allow the operator to determine the size of the instrument's measurement area on the target. For example, some instruments include sighting devices that approximately outline the measurement area so that an operator can more easily correlate the instrument's readings with the correct area of the target.
Thermal imagers or cameras with image displays provide an even greater degree of information. Images obtained using these cameras assign colors or gray-levels to the pixels composing the scene based on the intensity of the IR radiation reaching the camera's sensor elements. Thus, an operator can view the target in the infrared spectrum. However, because the resulting IR image is based on the target's temperature, and because the colors or levels displayed by the camera do not typically correspond to the visible-light colors of the scene, it can be difficult, especially for novice users of such a device, to accurately relate features of interest (e.g. hot spots) in the IR scene with their corresponding locations in the visible-light scene viewed by the operator. In applications where the infrared scene contrast is low, infrared-only images may be especially difficult to interpret.
To provide better identification of temperature spots of interest, some cameras capture a visible-light image of the scene using a separate visible-light camera built into the thermal imaging camera. Some of these thermal imaging cameras allow a user to view the visible-light image side-by-side with the infrared image. To make this comparison easier, some thermal imaging cameras now provide simultaneous viewing of the infrared image and the visible-light image overlapping each other and blended together.
Even when the infrared image and the corresponding visible-light image are overlayed and blended, identifying objects and temperature features within the images can be difficult due to, for example, low image resolution or problems in image alignment. Also, incorporating electronic displays (e.g., LCD) and/or visible-light sensors can add unneeded complexity and may be cost prohibitive in many instances. Accordingly, there exists a need for improved and/or less expensive identification systems for temperature measurement instruments.